Ellipsometer or Polarimeter and the like systems, allow determination of Sample System physical and optical properties, (such as thickness, refractive index and extinction coefficient of surface films thereon, by detecting change in the "Polarization State" of a beam of polarized light which is caused to interact with said Sample System, where Polarization State here refers to a set of values for Polarized Light Beam Quadrature Components, (such as "S" and "P"), Magnitude Ratio, and a Phase Angle therebetween. (It is noted that "P" refers to that component which is in a plane containing the normal to a Sample System and incident and/or transmitted beam(s) of polarized light, and "S" refers to that component perpendicular thereto and parallel to the surface of said Sample System. It is also noted that a "full" polarization state also requires designation of an absolute value to which a magnitude ratio is referenced, and the direction of rotation of a polarized beam of light).
Ellipsometer Systems generally can be broadly classified as Rotatable or Intensity Modulating Rotating Element Ellipsometers (REE) and Phase Modulating Modulation Element Ellipsometers (MEE). For instance, a Patent to Woollam et al., U.S. Pat. No. 5,373,359, describes a Rotating Analyzer Ellipsometer (RAE) in which a Light Source provided beam of light is caused to pass through a Polarizer, (which serves to set a Polarization State therein), then interact with a Sample System. Said interaction with said Sample System serves to alter the Polarization State of said polarized beam of light, which polarized beam of light then sequentially encounters a Rotating Analyzer and a Dispersion Optics, (e.g. a Diffraction Grating is specified), which forms therefrom a multiplicity of essentially single wavelength polarized beams of light. Said multiplicity of essentially single wavelength polarized beams of light are then caused to enter a Photo Detector Array, in which Photo Detector Array, individual Detector Elements serve to develop a representative signal for each. Fourier Analysis, for instance, of said signals allows determination of parameters which allow determination of Sample System characterizing PSI and DELTA values. It is noted that in said Woollam et al. (RAE) there is no additional focusing applied after the polarized beam of light encounters the Sample System. Another Patent, to Ducharme et al. U.S. Pat. No. 5,416,588, on the other hand, describes a Modulation Element Ellipsometer (MEE) comprised of a Light Source, a Polarizer, a Polarization State Modulator Element, a means for splitting Quadrature Components in a Beam of Polarized Light after interaction with a Sample System, two Detector Elements and an Analysis System. In use a beam of light is provided by the Light Source and a state of Polarization is set therein by said Polarizer, after which the polarized beam of light is subjected to a Polarization State Modulation and caused to interact with a Sample System, which Sample System changes the State of Polarization of said Phase Modulated Polarized beam of light. Quadrature Components of said Polarized beam of Light are then isolated and subjected to separate, for instance, Fourier Analysis. Appropriate utilization of the Coefficients of the terms of a Fourier Series allows determination of Sample System characterizing PSI and DELTA values. It is noted the described Modulation Element Ellipsometer (MEE) utilizes Coefficients from Fourier Series based upon both Quadrature Components. Some Modulation Ellipsometers utilize Fourier Series Coefficients based upon only one such Quadrature Component. While the specifics of signal generation are different in (REE) and (MEE) ellipsometers, and even amongst Ellipsometers of similar type, the end result of utilization thereof is provision of PSI and DELTA values for Sample Systems analyzed therein. This is the case regardless of Sample System type (e.g. isotropic, anisotropic or anisotropic and depolarizing).
In the above the terms Polarizer and Analyzer were utilized, and it is to be understood that said elements can be essentially similar and are identified primarily by location in an Ellipsometer or Polarizer and the like system. Polarizers are positioned ahead of a Sample System, and Analyzers thereafter. As well, Compensators can be present, for instance, between Polarizers and Analyzers, and after Analyzers. Compensators generally operate to change a phase angle between quadrature components of a polarized beam of light, via a birefringence property which serves to retard one quadrature component differently than the other. Polarizers, Analyzers and Compensators can be Rotatable, Rotating and Stationary in use.
Numerous other Ellipsometer Systems could be described, which are, for instance, comprised of various combinations of:
Stationary Polarizer(s); PA1 Stationary Compensator(s); PA1 Stationary Analyzer(s); PA1 Rotatable Polarizer(s); PA1 Rotatable Compensator(s); PA1 Rotatable Analyzer(s); PA1 Rotating Polarizer(s); PA1 Rotating Compensator(s); PA1 Rotating Analyzer(s); PA1 Modulator Element(s). PA1 a. Rotatable Element Nulling Ellipsometers (RENE); PA1 b. Rotatable Element Automated Nulling Ellipsometers (REANE); PA1 c. Modulation Element Ellipsometers (MEE); PA1 d. Rotating Analyzer Ellipsometers (RAE); PA1 e. Rotating Polarizer Ellipsometers (RPE); PA1 f. Rotating Compensator Ellipsometers (RCE); PA1 g. Rotating Polarizer and Analyzer Ellipsometers (RPAE); PA1 h. Rotating Polarizer and Analyzer, Fixed Compensator (RPAFCE); PA1 i. Rotating Analyzer and Compensator, Fixed Polarizer Ellipsometer (RACFPE); PA1 j. Rotating Polarizer and Compensator, Fixed Analyzer (RPCFAE); PA1 k. Rotating Analyzer, Fixed Polarizer and Compensator Ellipsometer (RAFPCE); PA1 l. Rotating Polarizer, Fixed Analyzer and Compensator Ellipsometer (RPFACE); PA1 m. Rotating Compensator, Fixed Analyzer and Polarizer Ellipsometer (RCFAPE); PA1 (Note that similar identifying descriptions also apply to Polarimeter and the like Systems).
Examples of Ellipsometers to which the present invention system and method of application can be applied are, for instance:
However, for the purposes of the present invention it is not necessary to describe each above listed system in detail. The present invention, while applicable to essentially any Ellipsometer or Polarizer and the like System, is focused upon the simultaneous production of a plurality of measureable Orders of essentially single wavelength polarized beams of light from a polychromatic beam of light, which polychromatic beam of light has been caused to interact with a Sample System. (Note that a Dispersive Optics actually provides a continuous spectrum of spacially separated wavelengths which are present in a Polarized Source Light Beam. It is convenient, however, to view said spectrum as a multiplicity of essentially single wavelength polarized beams of light. Such an approach has particular relevance where, because of size and placement, a Detector Element intercepts a relatively narrow band of said wavelengths centered about some wavelength in a physically realized system).
Continuing, the Woollam et al. U.S. Pat. No. 359 Patent identified above, presents a system of two Diffraction Gratings toward the end goal of the present invention, wherein a polarized beam of light Diffracted by one Diffraction Grating is caused to impinge upon another and provide a second spectrum of wavelengths. There exists, however, need for an improved approach to simultaneously providing a plurality of "Orders" per se. of polarized essentially single wavelength polarized beams of light. The reason for this is that simultaneous analysis of information in a plurality of essentially single wavelength polarized beams of light, which essentially single wavelength polarized beams of light are derived from a polychromatic polarized beam of light, which polarized polychromatic polarized beam of light has been caused to interact with a Sample System, allows more convenient characterization of more complex Sample Systems.
A paper titled "Division-Of-Amplitude Photopolarimeter Based on Conical Diffraction For a Metallic Grating" by Azzam, in Applied Optics, Vol 31, No. 19, 1 Jul. 1992 and U.S. Pat. No. 5,337,146 are also noted. The purpose of the System and Method of Use described in said references is to allow simultaneous measurement of all four Stokes Parameters of a Beam of Light. The System involved is a Gratting which serves to provide Four Orders, each of which must be intercepted, possibly by a Detector Array. While the present invention System is to some extent similar to that alluded to in said Azzam references, it is to be appreciated that the Purpose to which the present invention System speaks, and the Method of Use thereof are very different than that described by Azzam. As well, the Azzam System, while providing for Polarization of wavelengths in certain Orders, does not provide for the filtering-out of stray light or of overlapping portions of adjacent Orders to provide wavelengths of an Order free of any masking influence of wavelengths present in an adjacent Order. The present invention provides that multiple, element filters be present, which, in the context of spectroscopic ellipsometer or polarimeters and the like has not, to the inventor's knowledge, been previously known.
The present invention then, as taught supra in this Disclosure, is a multiple "Order" producing Dispersive Optics system and method of application thereof, for use in providing a multiplicity of essentially single wavelength polarized beams of light, in combination with Ellipsometers and/or Polarimeters and the like. The purpose thereof is to allow simultaneous detection and analysis of closely situated wavelengths, by interception thereof in different Multiple Order producing Dispersive Optics produced Orders, which closely situated wavelengths can not be simultaneously detected in a single Order because of Detector Element finite dimension limitations.